1. Field of the Invention
The present invention relates to a magnetoresistive element for regenerating a line of magnetically recorded information by taking advantage of an element in which electric resistance varies in response to changes of external magnetic fields. The present invention in particular relates to a magnetoresistive element and a method for producing the same, wherein flattening of the top face of the magnetoresistive element is attained without deteriorating regenerative characteristics.
2. Description of the Related Art
FIG. 7A is a cross section, in the vicinity of an ABS (Air Bearing Surface), of an AMR (Amisotropic Magnetoresistive) element for sensing recording magnetic field from a recording medium such as a hard disk device.
A so-called inductive type write magnetic head is laminated on this AMR element.
A soft magnetic layer (SAL) 20, a non-magnetic layer (SHUNT layer) 21 and a magnetoresistive layer (MR layer) 22 are laminated on the foregoing AMR layer from the bottom to the top and hard bias layers 24, 24 and lead layers 26, 26 are laminated on both side areas of this laminated body.
Interlayers 25, 25 for improving heat resistance are formed between the hard bias layer 24 and lead layer 26 with a protective layer 23 formed on the magnetoresistive layer 22. Both of the interlayers 25 and protective layer 23 are formed of Ta films.
Usually, a film of a Ni--Fe--Nb alloy is used for soft magnetic layer 20, a Ta film is used for the non-magnetic layer 21, a film of a Ni--Fe alloy is used for the magnetoresistive layer 22, a film of a Co--Pt alloy is used for the hard bias layer 24 and a Cr film is used for the lead layer 26.
The hard bias layer 24 functions as a magnet magnetized along the X-direction in this AMR element, a bias magnetic field being applied from hard bias layer 24 to the magnetoresistive layer 22 along the X-direction. A bias magnetic field is also applied from the soft magnetic layer 20 to the magnetoresistive layer 22 along the Y-direction. Applying bias magnetic fields to the magnetoresistive layer 22 along the X- and Y-directions allows magnetization changes of the magnetoresistive layer 22 to linearly respond against magnetic field changes.
A sensing current from the lead layer 26 is imparted to the magnetoresistive layer 22. Since the scanning direction of the recording medium such as a hard disk device is along the Z-direction, changes of the magnetization direction of the magnetoresistive layer 22 allows resistance values to be changed when a leakage magnetic field from the recording medium is applied along the Y-direction, which is sensed as voltage changes.
While an inductive head is laminated on the AMR element via a top gap layer (not shown in the drawing) as hitherto described, the inductive head is composed of a bottom core layer (top shield layer) 40, a top core layer 41 and a coil layer (not shown in the drawing).
When a recording current flows through the coil layer, a recording magnetic field is imparted to the top core layer 41 and bottom core layer 40, magnetic signals being recorded on the recording medium such as a hard disk device by a leakage magnetic field between the bottom core layer 40 and top core layer 41.
FIG. 9 is a cross section in the vicinity of the ABS of a spin-valve type thin film element (a spin-valve type thin film magnetic head) for sensing recording magnetic field from the recording medium such as a hard disk device. An inductive head composed of the bottom core layer 40 and the top core layer 41 shown in FIG. 7A is also laminated, though not shown in the drawing, on the spin-valve type thin film element.
The spin-valve type thin film element described above is a kind of GMR (giant magnetoresistive) element, having a better regeneration sensitivity than the AMR element for complying with the requirement of high density recording.
An underlayer 34 such as Ta, an antiferromagnetic layer 30, a fixed magnetic layer (a pinned magnetic layer) 31, a non-magnetic conductive layer 32 and a free magnetic layer 33 are laminated from the bottom to the top in this spin-valve type thin film element, and a protective layer 23 made of, for example, Ta is formed on the free magnetic layer 33 as in the AMR element shown in FIG. 7A.
Hard bias layers 24, 24 are formed, as in the AMR element shown in FIG. 7A, at both side areas of the laminated body from the underlayer 34 through the protective layer 23, lead layers 26, 26 being formed on these hard bias layers 24, 24 via the interlayers 25, 25.
A film of a Ni--Mn alloy, a film of a Ni--Fe alloy and a Cu film are usually used for the antiferromagnetic layer 30, pinned magnetic layer 31 and free magnetic layer 33, respectively.
The antiferromagnetic layer 30 and the pinned magnetic layer 31 are formed in contact relation with each other as shown in the drawing. The pinned magnetic layer 31 is put into a single magnetic domain state by exchange magnetic coupling at the interface with the antiferromagnetic layer 30, the magnetization direction of which being fixed along the Y-direction.
The magnetization direction of the free magnetic layer 33 is aligned along the X-direction by being affected by the hard bias layers 24, 24 magnetized along the X-direction.
A static current (sensing current) is imparted from the lead layers 26, 26 to the pinned magnetic layer 31, non-magnetic conductive layer 32 and free magnetic layer 33 in this spin-valve type thin film element. Since the scanning direction of the recording medium such as a hard disk device is along the Z-direction, magnetization of the free magnetic layer turns from the X-direction to the Y-direction when the leakage magnetic field from the recording medium is applied along the Y-direction. Electric resistance varies depending on the relation between changes of the magnetization direction in the free magnetic layer 33 and the pinned magnetization direction of the pinned magnetic layer 31. The leakage magnetic field from the recording medium is sensed due to voltage changes based on this electric resistance change.
Meanwhile, the film thickness of the leading layer 26, formed on both side areas of the laminated body from the soft magnetic layer 20 through the protective layer 23 as shown in FIG. 7A, is very thick in order to reduce the direct current resistance (DCR) of the AMR element. Small direct current resistance allows the sensing output to be large, improving the regenerative characteristics.
However, the overall thickness of the both side areas comprising the hard bias layer 24, interlayer 25 and lead layer 26 becomes thicker than the overall thickness of the laminated body (the layer from the soft magnetic layer 20 through the protective layer 23) when the film thickness of the lead layer 26 is made thick, resulting in a distorted configuration of the top face of the AMR element as shown in FIG. 7A.
Consequently, the bottom core layer 40 to be formed on the AMR element is deposited as a bent layer following the undulation of the top face of the AMR element as shown in FIG. 7A, also causing a distortion of the top core layer 41 in confronting relation over the bottom core layer 40 via a magnetic gap G.
When the portions of the bottom core layer 40 and top core layer 41 being in a confronting relation with each other via the magnetic gap G are distorted as shown in FIG. 7A, the recording patterns 42, 43 written on the recording medium becomes non-linear as shown in FIG. 7B with bent portions at both ends. Non-linear recording of the signals on the recording medium as described above causes the following problems.
Supposing that the recording medium travels from the face to the back of the drawing to regenerate the signals in the recording pattern 42, the signals in the recording pattern 43 outside of the signals in the recording pattern 42 are simultaneously regenerated at near the both ends of the magnetoresistive layer 22 as shown in FIG. 7B, causing a problem that a good regenerative characteristic cannot be attained.
Furthermore, it is another problem that projections (burrs) are formed at the site making a contact with the laminated body in the lead layer 26 when lead layer 26 has a large film thickness.
FIG. 8A is a cross section of the AMR element representing the production process for producing the AMR element.
In this production process of the AMR element, a lift-off resist layer 27 is deposited on the protective layer 23 after depositing a laminated body comprising a soft magnetic layer 20, a non-magnetic layer 21, a magnetoresistive layer 22 and a protective layer 23 on the substrate. Then, both sides of the laminated body are shaved off so that the both side faces of the laminated body assume inclined faces.
The hard bias layer 24, interlayer 25 and lead layer 26 are deposited thereafter on the both side areas of the laminated body, each layer being also deposited on the resist layer.
When the lead layer 26 is formed with a large film thickness in order to reduce direct current resistance, the lead layer 28 formed on the resist layer also has a large film thickness, thereby the lead layer 26 is formed in continuity with the lead layer 28 as shown in FIG. 8A.
When the resist layer 27 is removed while these two lead layers are in continuity, a part of the lead layer 28 remains on the lead layer 26 as projections (burrs) 29. FIG. 8B shows the partially enlarged drawing of the b-area shown in FIG. 8A after removing the resist layer 27.
The same problem as described above occurs in the case of the spin-valve type thin film element shown in FIG. 9.
The lead layer 26 of the spin-valve type thin film element has a so large film thickness that the film thickness at the both side areas of the laminated body becomes larger than the film thickness of the laminated body hitherto described, causing a distortion on the top face of the spin-valve type thin film element. Consequently, the bottom core layer 40 of the inductive head and the top core layer 41 to be formed on the spin-valve type thin film element are also formed with distortions, causing a problem that signals cannot be linearly recorded on the recording medium.
It is also a problem that projections (burrs) 29 are liable to be formed in the lead layer 26 as seen in FIG. 8B owing to a large film thickness of the lead layer 26.
FIG. 10 and FIG. 11 is an another example showing the structure of the conventional spin-valve type thin film element.
The construction of the both side areas of the spin-valve type thin film element in FIG. 10 is different from that of the both side areas of the spin-valve type thin film element in FIG. 9.
In FIG. 10, a first lead layer 35 is firstly formed on both sides of the laminated body from the underlayer 34 through the protective layer 23, bias layer 36 and the second lead layer 37 being laminated on the first lead layer 35.
Since a distortion has been introduced in the spin-valve type thin film element shown in FIG. 10 as in the spin-valve type thin film element shown in FIG. 11, the bottom core layer 40 and top core layer 41 formed on the spin-valve type thin film element are also distorted.
The hard bias layer 36 is formed without making a contact with the inclined face of the laminated body in the spin-valve type thin film element shown in FIG. 10 but the first lead layer 35 is placed between the hard bias layer 36 and free magnetic layer 33. Accordingly, the free magnetic layer 33 is hardly affected by the bias magnetic field from the hard bias layer 36, thereby magnetization of the free magnetic layer is not properly aligned along the X-direction to readily generate Barkhausen noise.
While the spin-valve type thin film element shown in FIG. 11 has a largely different structure from the spin-valve type thin film element shown in FIG. 9 and FIG. 10, the principle of regeneration is quite the same. The reference numeral of each layer in FIG. 11 corresponds to the reference numerals of the respective layers in FIG. 9 and FIG. 10.
The top face of the spin-valve type thin film layer shown in FIG. 11 is formed with a distortion like the top face of the spin-valve type thin film element shown in FIG. 9 and FIG. 10. Therefore, these structures are not preferable.
Since the spin-valve type thin film element shown in FIG. 11 is not adjusted to a desired shape by etching after depositing the laminated body from the free magnetic layer 33 through the antiferromagnetic layer 30 but its width is formed to be longer than the track width Tw, noises are easily picked up from the area outside of the track width region Tw during the regeneration operation, causing a problem that improvement of the regenerative characteristic is impossible.
Although the top face of the magnetoresistive element is not flattened in the construction of each conventional magnetoresistive element hitherto described, the top face of the magnetoresistive element is flattened in the two conventional examples to be described hereinafter.
FIG. 12 and FIG. 13 are cross sections showing the structure of the AMR element.
As shown in FIG. 12, lead layers 51, 51 are formed on both sides of the insulation layer 50, and the soft magnetic layer 20, non-magnetic layer 21 and magnetoresistive layer 22 are continuously laminated on the top faces of the insulation layer 50 and lead layer 51.
The soft magnetic layer 20 and the non-magnetic layer 21 are formed on the insulation layer 50 followed by laminating the lead layer 51 and hard bias layer 52 on both sides of this laminated body in the magnetoresistive element shown in FIG. 13. The magnetoresistive layer 22 is formed on the top face of the non-magnetic layer 21 and hard bias layer 52.
The top face of the magnetoresistive layer 22 corresponding to the uppermost layer of the AMR element is flattened as shown in FIG. 12 and FIG. 13. Consequently, the bottom core layer 40 and top core layer 41 formed on this AMR element are aligned in parallel relation to the soft magnetic layer 20, non-magnetic layer 21 and magnetoresistive layer 22. Therefore, the signals are almost linearly recorded on the recording medium to properly regenerate the signals by the AMR element.
Meanwhile, the magnetoresistive layer 22 is deposited on the top face of the non-magnetic layer 21 and elongated onto the hard bias layer in the AMR element shown in FIG. 12 and FIG. 13 with a wider width of the magnetoresistive layer 22 than the track width Tw. Accordingly, It is quite possible that the magnetoresistive layer 22 picks up noises from the area outside of the track width Tw during regeneration operation, thereby deteriorating the regenerative characteristic.
As will be evident from the foregoing discussions, we cannot find no inventions in which the top face of the magnetoresistive element is flattened without deteriorating the regeneration characteristic.